This invention relates generally to video tape recording apparatus, such as a VTR or VCR of helical scan type, and method for recording and/or reproducing video and audio signals on a magnetic tape by way of rotary heads.
In helical scan video tape recorders, two or more rotary heads are provided for recording and/or reproducing a video signal, while a stationary head is usaully provided for recoridng/reproducing an audio signal. Since the highest frequency of the audio signal recorded and subsequently reproduced from a video tape is determined by the relative velocity between the audio head and the tape, such a conventional audio recording/reproducing system using a stationary head is unsatisfactory in view of high-fidelity (Hi-Fi) audio reproduction. Especially, when a VTR is operated in a long-time mode, the tape travelling speed is reduced, and therefore, the relative velocity is also reduced causing deterioration in the quality of reproduced audio signals.
In order to provide a Hi-Fi audio reproduction by way of a helican scan video tape recorder, therefore, various approaches have hitherto been made. According to one conventional technique of a Hi-Fi system an audio signal is converted into a PCM signal to be superimposed on a video signal prior to recording so that a superimposed video and audio signals are simultaneously recorded on a video tape by way of one or more rotary heads. However, this approach is apt to suffer from the occurrence of moire on a reproduced picture due to beat interference between carrier frequencies of the audio and video signals since a frequency modulated audio signal is superimposed on a video signal including a frequency modulated luminance signal and low frequency-converted chrominance signal to be recorded by way of an identical head and subsequently reproduced by the same head.
The inventor of the present invention proposed a new technique for resolving such a conventional problem, and applied for patents in Japan, No. 58-2570 filed Jan. 11, 1983; in the United States, Ser. No. 567,977 filed Jan. 4, 1984; in United Kingdom, No. 8400,548 filed Jan. 10, 1984; and in West Germany, No. P34 00 720.2 filed Jan. 11, 1984. According to the proposed technique rotary heads used for recoring/reproducing only audio signals are provided in addition to rotary video heads so that audio signals are recorded first and then video signals are recorded upon prerecorded audio signals such that video tracks entirely cover audio tracks. Although this technique is satisfactory when prerecorded signals are playbed back at a standard playbak speed, when in long-time playback mode satisfactory audio signal reproduction cannot be performed due to crosstalk between adjacent audio tracks. Especially, crosstalk at low frequency range of audio signals is remarkable, and when such a superimposition techique is adapted to a recording system in which a chrominance signal is frequency modulated as in SECAM system, crosstalk reduction using phase-shift system utilizing correlation between phases of chrominance signals of consecutive horizontal periods does not satisfactorily operate because accurate correlation in phase of chrominance signal does not exist since the chrominance singal is a frequency modulated signal. Although influence by such crosstalk is negligible in standard-time mode because picked up signal level from a right track is sufficiently larger than the crosstalk components from adjacent tracks since each right track is adequately wide, the influence of crosstalk on long-time mode cannot be ignored since the track width is reduced to one half in the case of long-time mode which is twice the standard-time recording period. More specifically, when the track width is reduced to one half, then the signal level from a right track is also reduced to one half compared to the standard-time mode, and signal-to-noise (S/N) ratio is apt to deteriorate. Such deterioration in S/N appears as color signal noise in a reproduced picture. To prevent the occurrence of color signal noise therefore, a further improved technique was devised by the present inventor so that guard bands are provided between video tracks to reduce crosstalk in long-time mode while the width of video tracks is made smaller than one half the track width in standard-time mode.
However, if the width of audio tracks is also reduced in long-time mode together with width reduction of video tracks, S/N of reproduced audio signals deteriorates, and such method of recording cannot be used.